Optically active compounds of 3a, 8b-cis-dihydro-3H-cyclopenta[b]benzofuran derivatives as one of cycloalkyl-[b]benzofuran have been obtained by optical resolution of [7-bromo-3a, 8b-cis-dihydoro-3H-cyclopenta[b]benzofuran-5-il] formate using an optically active amine (Japanese Unexamined Patent Publication No. 59-161371), or by optical resolution of an intermediate compound with an enzyme (J. Chem. Soc., Chem. Commun. 811, 1995). However, the procedure becomes complicated since recrystallization is repeated by forming a complex in the optical resolution method using an optically active amine. In the optical resolution method using an enzyme, on the other hand, a dilute substrate concentration is used besides requiring a long reaction time. In addition, repeatability may be sometimes poor depending on the lot of the enzyme used.
The object of the present invention, based on the drawbacks of the conventional art, is to provide a useful process for producing desired optically active cycloalkyl[b]benzofuran by a cyclization reaction using a readily available optically active starting material.